This invention relates to a rotary actuator, particularly adapted for use in a device for driving a damping force adjusting mechanism of a hydraulic damper.
In adjusting the damping force of a hydraulic damper incorporated in a vehicle such as an automobile, to accommodate with the driving conditions, the conditions of the road and the like, a damping force adjusting mechanism is provided in the hydraulic damper. The damping force adjusting mechanism usually comprises a driving device for rotating an adjusting member which adjusts the opening of a liquid passage. Heretofore, a device including a rack and pinion mechanism for transferring the motion of a reciprocally movable solenoid to a rotating motion, a rotary actuator including a geared electric motor or the like has been used as the driving device for attaining a high accuracy in locating the adjusting member. At the present time, it is required that the driving device be compact in size for improving its mounting property on the vehicle and that the operating speed be high for accommodating changes in operating conditions. Further, recently it has been necessary to adjust the damping force in three or more steps and, accordingly, the driving mechanism is required to have three or more accurate stop positions.
However, the aforesaid reciprocally movable solenoid motor cannot satisfy such requirements since it is difficult to provide simple and reliable stop(s) at intermediate position(s). In the aforesaid rotary actuator, it is relatively difficult to reduce the size, the responsiveness of the geared motor is impaired when the reduction ratio is increased for reducing the size of the motor and, further, the mechanism and the control circuit are complicated. Therefore, prior art devices cannot satisfy the aforementioned requirements.
The present invention has been made in view of the aforesaid circumstances and, the object of the invention is to provide a rotary actuator which attains high accuracy in reliably locating three or more adjusting positions and which can reduce costs.